<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8">
  <style>
    legend {
      display: flex;
      width: 200px;
      height: 100px;
      overflow: scroll;
      border: 2px dashed gray;
    }
    div.child {
      background: lightblue;
      height: 1000px;
    }
  </style>
</head>
<body>
  <fieldset>
    <legend>
      <div class="child">
        There should be scrollbars making this area scrollable.
      </div>
    </legend>
  </fieldset>
</body>
</html>
